1. Field of the Invention
The present invention relates to a driving apparatus for an actuator.
Priority is claimed on Japanese Patent Application No. 2004-151601, filed May 21, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
Recently, some automobiles are equipped with an active control engine mount (which may be referred to as an “ACM” hereinafter) for reducing vibration of an internal combustion engine. Japanese Unexamined Patent Application, First Publication, No. H06-291379, published on Oct. 18, 1994, discloses such an ACM.
The active control engine mount is driven by an actuator utilizing, for instance, a solenoid or the like which is controlled by an actuator driving apparatus. The actuator driving apparatus controls the actuator to generate a vibration having a phase opposite to the vibration of the engine. It is required for the actuator to have a driving force and a response speed sufficient to support the engine and to respond to the vibration of the engine. Because of this requirement, the actuator is supplied with a driving voltage boosted or raised by a booster connected to and supplied with an electric source from an automobile battery.
Such a conventional actuator driving apparatus will be described with reference to FIG. 4.
An actuator driving apparatus 30 includes a boosting circuit 31 which boosts a voltage of an automobile battery (not shown) and a voltage dividing circuit 32 which divides the voltage boosted by the boosting circuit 31. The actuator driving apparatus 30 is equipped with a booster IC 33 which is connected to the voltage dividing circuit 32. The voltage dividing circuit 32 consists of resistors 35 and 36 which are serially connected between an output terminal of the boosting circuit 31 and a ground 34. The booster IC 33 is connected to a junction 37 of the resistors 35 and 36. An electromagnetic actuator 38 is connected to the output terminal of the boosting circuit 33. Thus, the booster IC monitors the voltage boosted by the boosting circuit 33 through the voltage dividing circuit 32 so as to hold the boosted voltage within a predetermined voltage range.
The actuator driving apparatus 30 thus constructed has the following problems because it operates such that the output of the boosting circuit 31 is held within a predetermined voltage range. That is, when the input voltage to the actuator driving apparatus 30 is decreased due to, for example, the decrease in the voltage of the automobile battery used as the electric source, the input current to the actuator driving apparatus 30 is increased so as to overheat the actuator driving apparatus 30. To prevent this, the operation of the boosting circuit 31 must be stopped.
Alternatively, to prevent or hinder the input current to the actuator driving apparatus 30 from increasing, it may be considered that an appropriate program for preventing the overheating be stored in the actuator driving apparatus 30 to cause the output current from the boosting circuit 31 to be reduced when the input voltage decreases. In the manner, however, the control for driving the electromagnetic actuator 38 would apparently be complicated.